The term “bio-fuel” refers to renewable energy sources obtained from various living or recently living biological materials, but generally excludes fossil fuels, which are also organic materials that have been transformed through geological process. Although they have their origin in ancient biological matter (“biomass”), they are not considered bio-fuels by the generally accepted definition because they contain carbon that has been “out” of the carbon cycle for a very long time. Plant and animal by-products can all be used as bio-fuels. Wood, forest residue, sawdust, yard clippings, domestic refuse, agricultural waste, shelled corn, non-food energy crops, animal fats, and dried manure can all be used as solid bio-fuels.
The burning of solid bio-fuel to generate heat began with the discovery of fire. Cut and split wood logs have been burned in furnaces for centuries and wood remains the most recognized and readily used type of solid bio fuel for heat production. Firewood and wood pellet furnaces are well known and commonly used for domestic heating applications. Bio-fuel furnaces have been developed for HVAC application and electrical power generation with limited success. Bio-fuel furnaces have also been developed specifically to incinerate a variety of residential, commercial, industrial and municipal waste products. Generally, these furnaces simply burn waste products for solely disposal purposes.
Conventional bio-fuel furnaces are limited to the types of bio-fuels that can be burned. Different bio-fuels have different ignition temperatures. Bio-fuels also have different moisture contents which effect the combustion process of bio-fuel furnaces. Heretofore, conventional bio-fuel furnaces used for waste incineration and energy generation have difficulty burning solid bio-fuel with high moisture content, which is generally more than fifteen percent (15%) moisture content. Normally, burning “dry” bio-fuels produces flame temperatures ranging between 900-1600° F. When bio-fuels having a high moisture content, that is generally exceeding fifteen percent (15%), are burned in conventional furnaces, steam is produced, which quickly reduces the temperature of the flame below the combustion temperature of the bio-fuel thereby extinguishing the flame.
In addition, conventional bio-fuel furnaces are limited to the amount of non-combustible materials that can be mixed with the bio-fuel. Noncombustible contaminants in the bio fuel can include sand, small rocks and gravel, metal scraps, glass and other inorganic material. Generally, conventional bio-fuel furnaces are limited to no more than a three percent (3%) mix of non-combustible materials in the bio-fuel. Non-combustible materials not only reduce the efficient combustion of conventional bio-fuel furnaces but can also damage the fuel feed augers, burn trough and other components. In the combustion process, at temperatures below 1600° F., non-combustible materials combine chemically to the non-combusted fuel particles resulting in a “clinker,” which is a lump of both non-combustible and un-combusted material. Clinkers block air-flow greatly reducing combustion efficiency and can eventually extinguish the flame.